The present disclosure relates to a detection apparatus, an electric power receiving apparatus, an electric power transmission apparatus, a wireless electric power transmission system, and a detection method that detect the presence of a conductor, such as a metal.
In recent years, the development of non-contact electric power transmission systems that supply electric power in a non-contact manner (wireless electric power supply) has been increasingly performed. Methods of realizing wireless electric power supply broadly include two types of techniques.
One of the techniques is an already widely used electromagnetic induction method, in which the degree of coupling between the electric power transmission side and the electric power receiving side is very high, and electric power supply is possible at high efficiency. However, it is necessary to maintain a coupling coefficient between the electric power transmission side and the electric power receiving side. Consequently, in a case where the electric power transmission side and the electric power receiving side are spaced apart from each other or in a case where there is a positional displacement, the electric power transmission efficiency (hereinafter referred to as an “inter-coil efficiency”) between the coil of the electric power transmission side and the coil of the electric power receiving side is greatly deteriorated.
The other technique is a technique called a magnetic-field resonance method in which a resonance phenomenon is actively used and thus, the magnetic flux shared by the electric power supply source and the electric power supply destination may be small. In the magnetic-field resonance method, even when the coupling coefficient is small, if the Q value (Quality factor) is high, inter-coil efficiency does not deteriorate. The Q value is an index (indicating the strength of the resonance of the resonance circuit) representing the relationship between the retention and the loss of energy of the circuit having the coil of the electric power transmission side or the electric power receiving side. That is, axial alignment between the electric power transmission side coil and the electric power receiving side coil is unnecessary, and there is advantage that the degree of freedom of the position and the distance of the electric power transmission side and the electric power receiving side is high.
In a non-contact or wireless electric power transmission system, an important element is one for heat generation countermeasures for metal foreign matter. Not limited to the electromagnetic induction method or the magnetic-field resonance method, when electric power supply is to be performed in a non-contact manner, in the case where a metal is present between the electric power transmission side and the electric power receiving side, an eddy current is generated, and there is a risk that the metal will generate heat. In order to reduce this heat generation, many techniques for detecting metal foreign matter have been proposed. For example, a technique using a light sensor or a temperature sensor is popular. However, in the detection method using a sensor, costs are incurred in a case where the electric power supply range is wide as in the magnetic-field resonance method. Furthermore, in the case of, for example, a temperature sensor, since the output result of the temperature sensor depends on the thermal conductivity in the surroundings thereof, design restrictions are imposed on the devices on the transmission side and on the reception side.
Therefore, a technique has been proposed in which the presence or absence of metal foreign matter is determined by observing a change in parameters (electric current, voltage, etc.) when metal foreign matter enters the space between the electric power transmission side and the electric power receiving side. With such a technique, it is not necessary to impose design restrictions, and costs can be reduced. For example, in Japanese Unexamined Patent Application Publication No. 2008-206231, a method of detecting metal foreign matter by using the degree of modulation at the time of communication between an electric power transmission side and an electric power receiving side has been proposed. In Japanese Unexamined Patent Application Publication No. 2001-275280, a method (foreign matter detection by DC-DC efficiency) of detecting metal foreign matter using eddy current loss has been proposed.